Tapioca wastewater treatment by contact stabilization process

Abstract

This research work was studied on tapioca wastewater treatment by contact stabilization process under technical cooperation project : INSA Toulouse France, Department of Sanitary Engineering Chulalongkorn University and Department of Industrial Works Ministry of Industry. A laboratory scale contact stabilization unit, received from INSA Toulouse which established at Department of Sanitary Engineering was operated at a period 400 consecutive days. The study was concerned both of the raw wastewater and partial degradable wastewater from waste stabilization pond. During the treating raw wastewater period, the process efficiency was normally more than 85%, under the nutrients controlled condition, but the problem of sludge bulking due to filamentous bacteria was observed and encountered in this period. The partial degradable wastewater from waste stabilization pons was investigated in two conditions, nutrient controlled condition and both of nutrient and trace element controlled condition. Sludge age was used as the controlled parameter of the system. The system operated at sludge age 20, 10, 5 and 2 days respectively. Then, the results showed that the contract stabilization process had maximum, process efficiency of 97%, at sludge age 20 days. The operation of the system under nutrient controlled condition (COD:N:P greater than 150:5:1) at sludge age values 10 and 20 days, the problem of sludge bulking due to filamentous bacteria was encountered through out these periods. It was found that the trace elements as: MgSo_4 , CaCl_2, FeCl_3 and KH_2PO_4 in solution has affected to restrict the population of filamentous bacteria which it could be get rid of sludge bulking problem. The recommended sludge age value is between 5-20 days under the nutrient and trace element controlled condition which equivalent to the specific substrate utilization ranging from 0.8-0.5 kg-COD/kg-MLVSS-day. Moreover, the SVI value of the process decreased exponentially as the sludge age increased. The ratio of VSS/SS decreased directly as the sludge age increased. The process efficiency still has capacity for wastewater treatment with the efficiency of 62% at sludge age 10 days when the contract time approached zero. The essential kinetic coefficients determination and design procedure for contact stabilization process has been purposed and recommended in this research work.